1. Field of the Invention:
This invention relates to an automatic tensioning control system for winding stator coils.
2. Description of the Prior Art:
In winding loops for stator coils the wire is usually wound around two pins with permanently formed 180.degree. bends around each pin in ideally straight wire sides between the bends. The force necessary to achieve these bends is provided by the tension force of the wire. Heretofore the tension force has been achieved in several ways, still in use, including the crudest methods, such as a spring-loaded rope around the grooved rim of steel acting as a brake to restrain rotation of the reel on a central shaft. Simple spring-loaded pressure plates gripping the wire and tensioning by means of sliding friction on the insulated wire is still used. A more advanced device uses an air cylinder with spring adjustment to apply pressure to drum brakes to restrain the rotation of the reel on a central shaft.
All known production systems for stator coils depend upon operator skill in judging when the tension is adequate to bend the wire around the pin, and the operator usually adjusts some kind of spring-loaded friction device to obtain a suitable tension. No calibration of friction force versus adjustment is provided because the friction force varies widely and even if the braking force were constant on the reel, the wire tension would increase by about 60%, as the wire is unwound from about 22-inch diameter down to 14-inch diameter on the reel. While the wire can withstand large variations in tension without sustaining serious damage, such variations in tension will alter the shape of the loop and excess tension makes insulation damage more probable.
Further, operators frequently spend a large amount of time, and waste copper in trying to get the tensions adjusted in several wires at once and often loop coils with two or three wires very tight and one or two wires nearly too loose for an acceptable loop with four wires (for example) in parallel. The operator can only judge wire tightness by pulling on the wires and the braking force usually changes as the brakes become heated due to friction.